Photopolymerizable compositions have been widely used in the fields of printing and electronic material as photosensitive lithographic printing plates, photosensitive materials (e.g. photoresist, hologram, etc.) and the like, because a tough film is obtained by enhancing the photocrosslinking degree and photosensitivity can be easily improved by correct selection of a photopolymerization initiating system. Recently, as computer and laser technologies are remarkably advanced, it is requested that an image information subjected to computer processing can be directly recorded on a photopolymerizable composition layer by a laser scanning exposure.
These photopolymerizable compositions generally contain a polymerizable compound (e.g. a compound having an ethylenically unsaturated double bond, etc.), a polymerization initiating system (e.g. photopolymerization initiator, sensitizer, etc.) and, optionally, an organic polymer compound having solubility or swelling characteristic to solvent, alkaline solution or water. For the photopolymerizable composition which is directly used for recording the image information by laser, it is requested to have a photosensitive wave length range even within visible light wave length range, high sensitivity and excellent stability, as significant properties.
In order to meet the requirement, various photopolymerizable compositions having the photosensitive wave length range within the visible light range are suggested. Most of them are combinations of radical polymerization initiators with light absorbing compounds and, for example, combinations of N-aryl-.alpha.-amino acids such as N-phenylglycine with light absorbing dyes such as coumarin dyes (Japanese Patent Kokai No. 63-180946), thioxanthene dyes (Japanese Patent Kokai Nos. 63-043133 and 1-126302) or cyanine dyes (Japanese Patent Kokai No. 1-287105)); a combination of N-aryl-.alpha.-amino acids with aminobenzylidenecarbonyl compounds (Japanese Patent Kokai No. 1-131205); a combination of triazine compounds with cyanine dyes (Japanese Patent Kokai No. 2-189548); combinations of hexaarylbisimidazoles and thiols with dyes (Japanese Patent Kokai No. 1-279903); a combination of iron-allene complex with p-aminophenyl unsaturated ketones (Japanese Patent Kokai No. 2-305806) and the like are reported.
All of the above photopolymerizable compositions have the photosensitive wave length range in visible range but photosensitivity is not sufficient. For example, when image recording is conducted at high speed by a low output air-cooled argon laser, the photosensitivity is too low to proceed and it is thus necessary to make the composition more highly photosensitive. However, when photosensitivity is made higher, storage stability is lowered because the deterioration of sensitivity or insolubilization due to dark reaction arises and, therefore, they were of no practical use.